Help needed to understand PHP Libsodium and how to export keys.

I'm trying to implement a solution using PHP and Libsodium.

I'm working off of this example:

// On Alice's computer:

$alice_box_kp = sodium_crypto_box_keypair();
$alice_sign_kp = sodium_crypto_sign_keypair();

    // Split the key for the crypto_box API for ease of use
    $alice_box_secretkey = sodium_crypto_box_secretkey($alice_box_kp);
    $alice_box_publickey = sodium_crypto_box_publickey($alice_box_kp);
    
    // Split the key for the crypto_sign API for ease of use
    $alice_sign_secretkey = sodium_crypto_sign_secretkey($alice_sign_kp);
    $alice_sign_publickey = sodium_crypto_sign_publickey($alice_sign_kp);

// On Bob's computer:

$bob_box_kp = sodium_crypto_box_keypair();
$bob_sign_kp = sodium_crypto_sign_keypair();

    // Split the key for the crypto_box API for ease of use
    $bob_box_secretkey = sodium_crypto_box_secretkey($bob_box_kp);
    $bob_box_publickey = sodium_crypto_box_publickey($bob_box_kp);
    
    // Split the key for the crypto_sign API for ease of use
    $bob_sign_secretkey = sodium_crypto_sign_secretkey($bob_sign_kp);
    $bob_sign_publickey = sodium_crypto_sign_publickey($bob_sign_kp);

// Optionally, you can reassemble a keypair string from a secret key and 
// public key pair:

$keypair = sodium_crypto_box_keypair_from_secretkey_and_publickey(
    $alice_box_secretkey,
    $alice_box_publickey
);

Basically, stuck on the part where I need to export the public keys so I can share them with another user.

Server A has a private and public key generating in code, but I don't know how to export it.
Server B has a private and public key generating in code, but I don't know how to export it.

Once exported, I will need to know how to import the keys so I can decrypt the messages.

I used to use open_ssl library which was straightforward, but my company desire to use the libsodium libraries now and I can't seem to find any functions to export the keys.